Talker in a balloon (6)
I believe the answer is:
gasbag
I believe this is a double definition.
'talker' is the first definition.
(I have seen 'Compulsive talker' mean 'gasbag' so perhaps 'talker' could also mean 'gasbag')
'balloon' is the second definition.
(thesaurus)
'in a' acts as a link.
(Other definitions for gasbag that I've seen before include "One who talks too much, or a balloon" , "Loudmouth - or balloon?" , "One going on" , "One who natters a lot" , "He likes to talk" .)